Process for removing acid components from organic liquids



Pa tented Apr. 13, 1948- PROCESS FOR' REMOVING AClD COMPO- NENTS FROM ORGANIC LIQUIDS Johan C. D. Oosterhout signer to The Texas Port Arthur, Tex., asompany,

New York, N. Y.,

a corporation of Delaware No Drawing. Application August 23, 1945,

Serial No. 612,292

This invention relates to a process for removing weakly acid-reacting organic substances from solutionsin organic liquids. More particularly, the invention relates to a process for the feznoval of mercaptans from petroleum distila es.

It is known to remove weakly acid compounds such as mercaptans, phenols and the like from pounds, i'or example, nitroethane, nitrobenzene;

liquid aliphatic amines, and pyridine.

As solutizers a variety of compounds soluble in alkaline solutions have been suggested. Many of these compounds are aliphatic monoor dicarboxylic acids. For example, alkaline solutions of isobutyric acid, particularly solutions of potassium isobutyrate in potassium hydroxide,

have been found to be especially valuable for use in the removal of mercaptans from petroleum distillates. Although aromatic carboxyllc acids have been considered for use as solutizers, the prior art shows that as a class these compounds are not suitable. Thus United States Patent No. 2,164,851 states that of the carboxylic acids possessing an aromatic ring phenyl acetic acid and its substitutes only are sufficiently soluble in strong caustic alkali solution to produce solubility enhancing efiects of practical value.

The alkali metal salts of phenyl acetic acid are said to be unique among even the salts of related phenyl-substituted aliphatic acids." This patent also shows that a true aromatic carboxylic acid, benzoic acid, is not suitable for use as a solutizer.

It is a principal object of the present invention to provide a novel and efficient process for the removal of weakly acid-reacting organic compounds from solution in non-acid water-insoluble organic liquids. A more specific object of the invention is to provide a process for the removal of a high percentage of mercaptans from petroleum ,distillates containing these acidic substances. a I

Other objects of the invention in part will be obvious andin part will appear hereinafter.

I have discovered, in accordance with the invention, that by extracting a solution of a weakly acid-reacting organic substance in a non-acid, water-insoluble organic liquid with an alkaline reacting solution containing a soluble salt of an 13 claims. (01. 196-30) alkylated derivative of the mono-nuclear aromatic carboxylic acids of the benzene series a high percentage of the acidic substance is removed from the liquid. For particular application to the removal of mercaptans from petroleum distillates the salts of alkylated mononuclear aromatic carboxylic acids containing from 1 to 8 carbon atoms in the alkyl radical, and in which the alkyl radical contains at least one tertiary carbon atom, as in the branched chain alkyl radicals, are preferred. The compounds of this class include the toluic acids, the isopropyl benzoic acids, the hydroxy isopropyl benzoic acids, the alleviated benzoic acids, such as the benzoic acids alkylated with isobutylene and di-isobutylene, and derivatives of such acids which contain substituents which do not alter the characteristic properties of the acids, particularly hydroxy, amino and like substituents.

Thus. I have found that cumic acid, p-isopropyl benzoic acid, in the form of its alkali metal salts is remarkably effective in enhancing the capacity of aqueous alkaline solutions for removing mercaptans from solution in petroleum distillates. The effectiveness of cumic acid in increasing the solubility of mercaptans in aqueous alkaline solutions does not appear to be explainable on the basis of relative solubility in caustic alkalis, since cumic acid salts are only slightly more soluble in alkaline solutions than corresponding salts of benzoic acid, which are sub-- stantially ineffective.

In carrying out the present process the organic liquid to be treated is mixed with an alkaline solution of a strong base, containing the carboxylic acid in the form of a salt oi. the alkaline element or radical. While present experience in- .dicates that solutions of sodium hydroxide and potassium hydroxide are superior to other alkaline solutions and are preferably used in the process, the invention includes the use of solutions of such strong bases as alkaline earth hydroxides, quaternary ammonium bases, alkali metal carbonates and bicarbonates, and the like.

Depending upon the extent of mercaptan removal desired, the extraction may be carried out in one stage or several stages. The organic liquid and the alkaline solution may simply be mixed and then allowed to settle into two layers which are then separated, or the organic liquid may be passed through a tower provided with means for accomplishing adequate mixing,

such as glass beads or Raschig rings, containing the alkaline solution. When operating in this way the passage of organic liquid through the tower is continued until the percentage removal of mercaptans falls to an undesirable level. The process may be carried out efiectively at room temperatures and these temperatures are gener- (a) An aqueous solution 2.8 N with respect to potassium hydroxide and 1.7 N with respect to potassium cumate;

(b) An aqueous solution 5 N with respect to po-- tassium hydroxide and 3 N with respect to potassium isobutyrate; and An aqueous solution 1.86 N with respect to potassium hydroxide and 1.13 N with respect to potassium benzoate.

In making up solutions a and c, the potassium hydroxide and the potassium carboxylate were first combined in the proportions which would correspond to a 5 N solution of potassium hydroxide and a 3 N solution of potassium salt upon the addition of the correct amount of water. It was found, however, that in order to dissolve the potassium salts it was necessary to add water in proportions to give aqueous solutions of the concentrations indicated.

Each of these three solutions was mixed intimately with cracked naphtha distillate, the resulting mixture was allowed to settle and the distillate was then separatedand tested for mercaptan sulfur content. It was found that the distillate treated with solution a contained only a trace of mercaptans, corresponding to more than 99 per cent complete removal or mercaptans; the distillate treated with solution 11 containing 0.0144 gram per liter of mercaptan sulfur, corresponding to an 87.4 per cent removal of mercaptans; and the distillate treated with solution 0 containing 0.0384 gram per liter of mercaptan sulfur, corresponding to 66.6 per cent removal of mercaptans. The amount of mercaptans removed by the use of solution 0, containing potassium benzoate, was about the same as could be removed by means of a strong caustic wash.

Two other treatments were carried out in a similar manner for removing mercaptans from a cracked naphtha distillate containing 0.0576 gram per liter of mercaptan sulfur. One sample of the distillate was treated at room temperature with 15 per cent by volume of a 2.9 N aqueous solution of potassium hydroxide, and the other sample was treated with an aqueous solution 2.8 N with respect to potassium hydroxide and 1.7 N with respect to potassium cumate. After the treatment, the first sample was found to contain 0.0208 gram per liter of mercaptan sulfur, corresponding to about a 63.8 per cent removal of mercaptans, while the second sample gave a negative doctor test indicating substantially zero mercaptan content.

Although the above results show that aqueous solutions of potassium hydroxide and potassium cu'mate containing less potassium hydroxide than has previously been considered most desirable are entirely suitable, it will be understood that stronger solutions may be used if desired.

Additional tests have been conducted to determine the efiectiveness of sodium cumate with V varying concentrations of sodium hydroxide and potassium cumate in lower concentrations of potassium hydroxide. The following results were obtained in the extraction of synthetic solutions of mercaptans in cleaners naphtha. Solutions of propyl, butyl and amyl mercaptan were prepared containing 3.8 grams of propyl mercaptan per liter. 4.5 grams of butyl mercaptan per liter, and 1.04 grams of amyl mercaptan per liter. These solutions were then treated at room temperature with 20% by volume of the extractant solution, by mixing intimately and allowing to settle, after which the naphtha was separated and tested for mercaptan sulfur content by titration with silver nitrate. In those experiments in v which the total mercaptan sulfur content was not removed the naphtha solution was again subjected to the foregoing treatmentand quantitative determinations of the amount of sulfur removed in the second extraction were made.

Mercaptan Concentration in Napbthe Propyl .38 But 1 .45 Am i 1.04 Extractant alteraitr- 8317M)? 1st 2d 1st 2d 1st 2d Ext. Ext. Ext. Ext. Ext. Ext.

Per Per Par Par Par Par can! can! ,cent cent cent cent 1.7N Sodium Cumate 55 68 68 83 1.7 N Sodium Oumate in 0.1 N NaOH 58 91 56 65 1.7 N Sodium Oumate in 0.2 N NaOH 79 100 62 89 1.7 N Sodium Cumate in OANNBOH 100 78 100 89 07 1.7 N Sodium Cumate+ LONNaOH 100 100 95 1.7 N Potass. Cumate 77 77 1.7 N Potass. Climate in It has been found that the treating solutions of the present invention can be regenerated satisfactorily by known methods. For example, a solution of potassium cumate in aqueous potassium hydroxide has been regenerated successfully simply by boiling the solution while adding water to maintain a constant volume. Other methods of regeneration, such as a. method involving blowing steam through the spent solution, can be used.

It will be understood that the present process is not limited to the use of substantially pure carboxylic acids of the class described.- For example, a caustic solution comprising an alkali metal salt oi. cumic acid may be prepared by oxidizing crude or relatively pure isopropyl toluene in known manner, for example, by blowing with air in the presence of lead oxide, removing the catalyst, as by treating with an acid where a catalyst such as lead oxide has been used, and then washing the oxidized material with a caustic solution to form a resulting caustic solution containing an alkali metal salt of cumic acid. The invention includes the use of solutions prepared in this way and by similar methods. The isopropyl toluene used in this method may be produced by alkylating toluene derived from cracked naphtha or straight run gasoline. with propylene, or by alkylating a 200 to 260 F. naphtha or gasoline cut with propylene, for example, under conditions similar to those used in the manufacture of cumene.

The process of the invention is entirely satisfactory when carried out with the use of alkaline solutions containing only one of the carboxylic acid salts. However, if desired, the solutions may also contain a hydroxy aromatic compound soluble in the alkaline solution, especially aallliyl phenols in the form of their alkali metal s ts.

This application is a continuation-in-part of .solved and which is substantially inert toward caustic alkali under the conditions of the process,

comprising extracting said water-insoluble organic liquid with an aqueous alkaline solution of a salt of an alkyl substituted mono-nuclear aromatic mono-carboxylic acid of the benzene series, under conditions to absorb at least a portion of said weakly acid-reacting compounds in the aqueous solution. I

2. The process of separating mercaptans from a hydrocarbon liquid in which they are dissolved, comprising extracting said hydrocarbon liquid with an aqueous alkaline solution of a salt of an alkyl substituted mono-nuclear aromatic monocarboxylic acid containing from 1 to 8 carbon atoms in the alkyl radicals thereof, under such conditions that at least a portion of said mercaptans is extracted into the aqueous solution.

3. The process of separating mercaptans from a hydrocarbon liquid in which they are dissolved, comprising extracting said hydrocarbon liquid with an aqueous alkaline solution of a salt of an alkyl substituted mono-nuclear aromatic monocarboxylic acid in which the alkyl substituents contain at least one branched chain alkyl group and from 1 to 8 carbon atoms, under such conditions that at least a portion of said mercaptans is extracted into the aqueous solution.

4. The process of separating weakly acid-reacting compoundsfrom a non-acid water-insoluble organic liquid in which they are dissolved and which is substantially inert toward caustic alkali under the conditions of the. process, comprising extracting said water-insoluble organic liquid with an aqueous alkaline-solution oi. an isopropyl substituted mono-nuclear aromatic mono-carboxylic acid, under such conditions that at least a portion of said weakly acid-reacting compounds is extracted into the aqueous solution.

comprising extracting said hydrocarbon liquid with an aqueous alkaline solution of an alkali metal salt of an isopropyl substituted mono-nuclear aromatic mono-carboiwlic acid, under conditions to absorb at least a portion of said mercaptans in the aqueous solution.

7. The process of separating mercaptans from a hydrocarbon liquid in which they are dissolved, comprising extracting said hydrocarbon liquid with an aqueous solution of an alkali metal hydroxide containing an alkali metal salt of an alkyl substituted mono-nuclear aromatic monocarboxylic acid, under conditions to absorb at least a portion of said mercaptans in the aqueous solution.

8. The process of separating mercaptans from a hydrocarbon liquid in which they are dissolved, comprising extracting said hydrocarbon liquid withan aqueous solution of an alkali metal hydroxide containing an alkali metal salt of an isopropyl substituted mono-nuclear aromatic mono-carboxylic acid, under conditions to absorb at least a portion of said mercaptans in the aqueous solution.

9. The process of separating weakly acid-reacting compounds from anon-acid water-insoluble organic liquid in which they are dissolved and which is substantially inert to caustic alkali under the conditions of the process, comprising extracting said water-insoluble organic liquid with an aqueous solution of a strong base containing in solution a salt of cumic acid, under conditions to absorb at least a portion 01' said weakly acidreacting compounds in the aqueous solution.

10. The process of separating mercaptans from a hydrocarbon liquid in which they are dissolved. comprising extracting said hydrocarbon liquid with an aqueous solution of an alkali metal hydroxide containing an alkali metal salt or cumic acid, under conditions to absorb at least a portion of said mercaptans in the aqueous solution.

11. In the process of separating mercaptans from a hydrocarbon liquid in which they are dissolved, involving extracting said hydrocarbon liquid with an aqueous solution of a strong base to remove mercaptans from said hydrocarbon liquid, the improvement which comprises incorporating in the said aqueous solution an alkali metal salt of cumic acid.

12. The process oi separating mercaptans from a sour petroleum distillate which comprises -extracting said distillate with an aqueous solution of potassium hydroxide containing potassium cumate in solution, to form an aqueous layer comprising said aqueous solution and absorbed mercaptans and a hydrocarbon layer consisting essentially or treated petroleum distillate, and separating said layers.

13. The process of separating weakly acid-reacting compounds from a hydrocarbon liquid in which they are dissolved, comprising extracting said hydrocarbon liquid with an aqueous solution ofa strong base containing in solution a salt oi. cumio acid, under conditions to absorb at least a portion or said weakly acid-reacting compounds in the aqueous solution.

JOHAN C. D. OOSTERHOUT.

summons 0mm The ioliowing references are of record in the iile or this patent:

UNITED STATES PATENTS 

